The present invention relates to rotating disk data storage devices, and in particular, to improving the tolerance of such data storage devices to vibration and other environmental stresses.
The latter half of the twentieth century has been witness to a phenomenon known as the information revolution. While the information revolution is a historical development broader in scope than any one event or machine, no single device has come to represent the information revolution more than the digital electronic computer. The development of computer systems has surely been a revolution. Each year, computer systems grow faster, store more data, and provide more applications to their users.
The extensive data storage needs of modern computer systems require large capacity mass data storage devices. While various data storage technologies are available, the rotating magnetic rigid disk drive has become by far the most ubiquitous. Such a disk drive data storage device is an extremely complex piece of machinery, containing precision mechanical parts, ultra-smooth disk surfaces, high-density magnetically encoded data, and sophisticated electronics for encoding/decoding data, and controlling drive operation. Each disk drive is therefore a miniature world unto itself, containing multiple systems and subsystem, each one of which is needed for proper drive operation. Despite this complexity, rotating magnetic disk drives have a proven record of capacity, performance and cost which make them the storage device of choice for a large variety of applications.
Rotating magnetic disk drives were originally installed in so-called mainframe computing environments, which typically maintained a very controlled environment. I.e., due to the complexity and sensitivity of the various computer system components, temperature, humidity and other factors were maintained within a narrow range. However, as computing machinery has become more ubiquitous, it has been necessary to design components which will tolerate a wider range of environments. Thus, disk drive storage devices have progressively been designed for use in desktop personal computers, and eventually in laptop and other portable devices.
Given the advantages of rotating magnetic disk drives, it would be desirable to use such devices in an even greater range of applications. One potential area of application is in on-board data storage permanently installed in an automobile.
As is well known, modem automobiles are incorporating ever greater electronic capabilities. A modern automobile typically contains an on-board processor, on-board memory in the form of semiconductor memory, and various I/O devices such as sensors, gauges, control mechanisms, warning systems, and the like. Thus, while it is not always recognized as such, a modem automobile contains all the components which define a basic computer system. It would be desirable to use this on-board computer system for an even greater range of tasks than is typical today. These tasks may be related to the function of the automobile itself, or may simply be tasks for the convenience of the driver or passengers, such as providing entertainment, news, or other information.
When the on-board computing system of a typical automobile is compared with that of a desktop computer, one glaring deficiency of the typical automotive computing system is data storage. A typical desktop system contains one or more rotating magnetic disk drive storage devices, capable of storing massive amounts of data. The automotive system typically does not, and is thus generally used for tasks which do not require this magnitude of data storage. The incorporation of disk drive storage in the on-board systems of automobiles would open up a new range of capabilities for such systems.
Although cost is a potential concern, the primary concern with incorporating magnetic disk drive storage devices in automotive systems appears to be the ability of such drives to operate satisfactorily in an automotive environment. Such an environment may involve exposure to temperature extremes, vibration, shock, noxious gases, and other environmental stresses which are not present in typical desktop, or even laptop, installations.
Therefore there is a need for modifications to the design of disk drive storage devices which enhance the ability of such devices to operate in severe environmental conditions, particularly, the conditions experienced in a motor vehicle installation.
In accordance with the present invention, a disk and spindle motor assembly of a rotating disk drive data storage device is constrained from freely rotating when not in use. Constraining free rotation reduces fretting of the spindle assembly bearings in the presence of vibration.
In the preferred embodiment, the disk drive is a rotating rigid magnetic drive of a type having a head load/unload mechanism, which typically leaves the disks free to rotate when the drive is powered down and the heads are unloaded.
Preferably, a small electric current is driven through at least one of the spindle motor drive coils to hold the spindle assembly in a fixed angular position while the disk drive is not in use. The spindle motor is a brushless DC motor, in which the stator comprises multiple electrical windings each associated with a respective phase, and the rotor comprises permanent magnets which respond to magnetic fields generated by the stator. Preferably, a conventional three phase design is used, each phase being driven by a separate drive transistor or transistors. Under normal operating conditions, these transistors are activated in sequence under control of a processor. When the drive is to be constrained, at least one of the drive transistors for a phase is activated. Preferably, fewer than all, and possibly only one, of the drivers is activated at any one time. The amount of current driving the coil will vary with the disk drive design and the force required to hold the spindle motor in place. In order to avoid degrading conditions which may be associated with holding the spindle assembly at any one position over a long period of time, the assembly is preferably rotated periodically to a different angular position by driving a different phase of the stator.
In the preferred embodiment, the spindle motor is not driven at all times when not in use. Instead, the drive may be in an xe2x80x9coffxe2x80x9d state in which no constraining force is applied. The disk detects a potential vibration condition, and activates one of the drive transistors to hold the spindle assembly in place only when required. Detection of a vibration condition may be achieved with a physical vibration sensor which senses actual vibration, or may be a response to an event which is likely to cause vibration, such as the ignition switch of an automobile being turned on. In this manner, for example, a disk drive within a car which is parked without the motor running might not need vibration protection, while the sensor will activate a drive transistor when the motor is running.
In an alternative embodiment, disk constraining may be achieved by mechanical means employing a mechanical braking arm or the like.